1. Field of the Invention (Technical Field)
The present invention relates to the use of bridging molecule complexes to covalently bond nanotubes and to use nanotubes for the formation of composite materials comprising functionalized nanotubes and organic based monomers and/or polymers.
2. Background Art
Carbon nanotubes are inert but can be chemically functionalized. Functionalization and derivatization increases interfacial binding in composites thus providing a mechanism for connecting nanotubes together and/or to substrates. Because of the limited scope of direct covalent sidewall functionalization at defect sites, traditional chemical treatments such as wet oxidation in concentrated HNO3/H2SO4 are used to functionalize nanotube surfaces with hydroxyl (—OH), carboxyl (—COOH) and carbonyl (>C═O) groups. In the art, carboxylic groups have been converted to acid chloride using thionyl chloride with subsequent amide linkage of an aminoalkanethiol to single-walled nanotubes (“SWNT's”). More recently SWNT's have been derivatized by thionyl chloride to produce thiols on the ends of SWNT's.
Polymer/nanotube nanocomposites are of interest because of their potential structural and electronic applications. However, the chemical interaction between polymers and nanotubes is typically limited to van der Waals forces and weak electrostatic interactions. It is known in the art that functionalization enhances the interaction between nanotubes and other organic matrices.
The fundamental control over composite morphologies and interfacial chemical interactions is critical for dramatically enhancing their performances in electronic applications. Although covalent attachment of polymers to nanotubes has been achieved, high loadings with poor nanotube dispersions dominate composite formation and device fabrication. Ion-conducting polymers, or polymers containing conductive fillers such as carbon black (5-30% by weight loading), are typically employed for electronic applications. However, they suffer from several drawbacks including having high dopant or filler loadings, being brittle, and being opaque as thin films. Carbon nanotubes offer a viable alternative. However, although single-walled carbon nanotubes (SWCNT's) provide the highest conductivities at low loadings, homogeneous dispersion is still problematic. In the prior art, multi-walled carbon nanotube (“MWCNT”) composites have offered a similar electronic potential to SWCNT's, but the loadings have been considerably higher, and the conductivities obtained have been considerably lower. Nanotubes in polymer composites do not have higher conductivities because of aggregation and tube-to-tube proximity. The result is that charge transport is via a hopping process where the charge carrier motion is determined by scattering from one conductive site to the next. Therefore, poor nanotube dispersion aggravates the poor and reduced carrier transport capability of the composite.